Prostate cancer (PCa) is the most frequently diagnosed non-skin malignancy for men in the United States. Studies have shown that it is necessary to treat 48 men to prevent one death from PCa, suggesting that significant overtreatment exists. On the other hand, in 2010 more than 32,000 men died of PCa. Surgery and radiation therapy can achieve excellent cancer control, but both surgery and radiation therapy are associated with adverse effects and an increased burden to our healthcare system. Alternative management options evolved, such as active surveillance (watchful waiting) and focal ablations. Yet these alternative management options rely heavily on biopsy. The current transrectal ultrasound-guided (TRUS) prostate biopsy, however, has significant shortcoming and high false-negative rates, largely related to targeting inaccuracies.
Many biopsy navigation devices for TRUS and 3D probes have been proposed to guide the biopsy. These biopsy navigation devices address several targeting error components but are commonly affected by prostate deformations, which are difficult to account for and to quantify. These errors may be relatively large. In fact, these errors can be larger than the radius of a “clinically significant” PCa tumor, and therefore, these errors alone can deteriorate the targeting plan.
Several technologies have been proposed to improve prostate biopsy. These technologies include 3D sonography, probe position tracking, image-fusion, and robotics. Using 3D ultrasound not only provides images of the prostate region, but also helps the physician's mnemonic perception of the anatomy and potentially improves his/her ability to sample the prostate more uniformly. For 3D ultrasound, multi-plane images are acquired by sensor arrays or using a mechanism that moves a sensor within the probe. Sensor array probes produce faster 3D acquisition but image quality and resolution tend to be lower because of space constraints, limiting the ability to guide the biopsy, because anatomic landmarks are more difficult to distinguish. Internal motion scanning probes preserve 2D image quality but have longer acquisition times, making it difficult to guide the intervention in real-time.
Several methods of tracking (continuously measuring) the location of TRUS probes have been proposed. Probe location is first used to render in 3D the prostate volume scanned by the images and then use these images to provide navigation to guide the biopsy. Optical and electromagnetic position trackers have been adapted to measure the location of the TRUS probe.
However, these systems generally require the use of a transperineal biopsy path or cause deflections of the prostate. The transperineal path is rarely used for biopsy because it causes more discomfort for the patients. This approach uses numerous biopsy cores, up to 100, and is performed in the operating room under anesthesia. However, to date this remains the most comprehensive way of biopsy because it gives more control on biopsy localization. But, for most of the biopsy patient population-at-large, the transperineal biopsy is logistically and economically unfeasible. Thus, there is a critical need for more accurate devices to perform the common TRUS-guided transrectal biopsy.
Current freehand TRUS-guided prostate biopsy inherently moves and deforms the gland (displacement+deformation≡deflection). Typically, the TRUS probe causes variable deflection of the gland while imaging. The resulting images are distorted, and the volume is skewed and not entirely reliable if rendered in 3D. Deflections are very difficult to quantify and correct.
Several common TRUS imaging planes and biopsy paths are included in FIGS. 1A-1E. These schematics aim to explain the types of prostate deflections. FIG. 1A shows the current standard of care. A 2D TRUS probe typically uses an end-fire sector ultrasonic sensor. A needle-guide adapter is attached parallel to the probe to guide the needle within the plane of the sensor, so that needle insertion can be seen in ultrasound. The probe is freehanded by the physician, who first moves the probe to understand the 3D anatomy, and second aligns the probe for each biopsy based on a mnemonic plan. Alignment is held with one hand while the other inserts the needle and triggers the biopsy. This is a very common but difficult task with subjective planning, navigation, and quality control. Among the problems is that prostate deflections are inexorable because the sensor must keep in contact with the rectum for the sonic waves to propagate. Pressing against the rectum deflects the prostate, more or less depending on the ultrasound coupling gel and physician's handling abilities. The schematic shows a simple indentation, but in reality deflections may be complex. While freehanded, it is nearly impossible to maintain the state of deflection while imaging and taking the biopsy.
With 3D and/or tracked TRUS the probe is still freehanded. Navigation and/or 3D are very helpful for the physician, but prostate deflections and derived skewed image problems remain. This is also the case for TRUS-MRI fusion based on freehanded TRUS, deflections further deteriorating fusion accuracy.
For the accuracy of image-guided biopsy targeting it is essential that the scanned volumetric images are geometrically accurate, and at the time when the biopsy is targeted the prostate has not geometrically changed from its initially imaged state, based on which the biopsy plan was made. If a certain level of compression is necessary for sound wave propagation, the same level must be maintained throughout. Several systems achieve this requirement for imaging and/or transperineal biopsy and brachytherapy.
Brachytherapy stabilizers were the first devices to support the probe. Here, probes use primarily a transverse ultrasound sensor, as illustrated in FIG. 1B. Images are scanned by stepping the probe in and out. As illustrated, this may also induce deflections at the end of the probe, but these should be somewhat repeatable at the same depth. The needle is passed transperineally through a needle-guide template of parallel holes. Transrectal needle access is unfeasible.
An essential advance was the addition of a fixed protective tubular cover, illustrated in FIG. 1C. The stepper now moves the probe within the cover so that the state of prostate deflection is preserved. This approach was first used by the TargetScan system and scan motion was motorized. The BioXbot adds robotic motion for the needle as well. Both work on the transperineal path.
TargetScan has also made a transrectal needle-guide adapter, but the only way to target the prostate was to bend the needle, as illustrated in FIG. 1D. However, that was problematic because core biopsy needles have internally moving parts which may jam if bent. But perhaps more difficult to account are targeting errors. When a needle is curved the amount of resistance encountered at the needle point contributes to its curvature making targeting uncertain when passing the heterogeneous tissues.
Recently, an alternative to the protective tubular cover was implemented on the University of Western Ontario robot by using a lateral-fire probe and with a purely rotary scan, as shown in FIG. 1E. Prostate deflections are preserved because the probe is round and well lubricated by the ultrasound coupling gel. This approach can be used for TRUS-guided prostatectomy. Most recently this approach was also used in a robot for prostatectomy navigation and elastography at the University of British Columbia, Vancouver, Canada.
An apparent problem with the lateral-fire rotary scan approach is that it can't be used for transrectal biopsy. However, it was observed that an oblique trajectory of the needle relative to the probe allows a straight needle to target the prostate, as shown in FIG. 1F. For this approach however, the needle must cross the shaft of the probe, which is not possible with current probes. There appears to be only one probe that presents a lateral slot on the side of the shaft, the BK Medical 8818. However, this probe does not have a lateral-fire sensor. Moreover, the needle-guide is locked to the probe thus inducing deformations when aligning for biopsy. Another possible approach is to pass the needle oblique but on the probe side. However, this is problematic because the needle may injure the anus and cause significant discomfort, and because the needle will lie outside the ultrasound plane making it difficult to monitor.
It would therefore be advantageous to provide a new TRUS probe for imaging the prostate with minimal deflection and an oblique path for the needle to follow for biopsy, thus allowing for an accurate transrectal biopsy path.